1. Field of the Invention
The present invention relates to a driver circuit configured to output a signal via a transmission line.
2. Description of the Related Art
In order to transmit a multi-valued level signal to a semiconductor device connected via a transmission line, a multi-valued driver is employed. Typical examples of such a multi-valued driver, which is configured to output a voltage Vdd that corresponds to high level and a voltage Vss that corresponds to low level, include a buffer (inverter) including a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an N-channel MOSFET connected in a push-pull manner.
FIG. 1A is an equivalent circuit diagram which shows a schematic configuration of a multi-valued driver circuit, and FIG. 1B is an operation waveform diagram showing the operation of the multi-valued driver circuit. An output port Po of a multi-valued driver circuit 200 is connected to an unshown device via a transmission line 202. The multi-valued driver circuit 200 is configured to selectively output one from among a high-level voltage VIH, a low-level voltage VIL, and a terminal voltage VTT, according to a selection signal s0 through s2.
The multi-valued driver circuit 200 includes a selector 204, a buffer 206, and an output resistor Ro. The selector 204 is configured to receive, as input signals, three voltages, i.e., VIH, VIL, and VTT, via three input terminals (0, 1, 2), respectively. The selector 204 is configured to select one from among the three voltages VIH, VIL, and VTT, according to a 3-bit selection signal s0 through s2. For example, such three voltages VIH, VIL, and VTT, having three respective values, are generated by an unshown D/A converter or the like. When the selection signal component s0 is asserted (set to high level), the selector 204 outputs the terminal voltage VTT. When the selection signal component s1 is asserted, the selector 204 outputs the high-level voltage VIH. When the selection signal component s2 is asserted, the selector 204 outputs the low-level voltage VIL. The buffer 206 is configured to receive the voltage thus selected by the selector 204, and to output the voltage thus received to the transmission line 202 via the output resistor Ro.